Biology 105 Evolution Dr Theodore Garland Jr 5

Biology 105 - Evolution Dr. Theodore Garland, Jr. 5 Nov. 2015: "Hybrid Zones, Character Displacement, Geographic Variation and Clines" Accompanies pages 467 -469 and 65 in: Bergstrom, C. T. , and L. A. Dugatkin. 2012. Evolution. W. W. Norton and Company. 1

Remember the Biological Species Concept (1) “Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. ” (Mayr, 1942) This is the definition you are most likely to be familiar with. 2

Remember the Biological Species Concept (2) This definition implies that species are real, discrete entities. Species 1 Species 2 3

Remember the Biological Species Concept (3) Evolutionarily, it defines a species as the smallest collection of individuals that evolve independently of others. Specifically, it states that species do not exchange genes with one another. ! o N 4

Hybrid Zones Geographically restricted areas between subspecies or species where hybrids are common May indicate: 1) partially reproductively isolated populations that have come back into contact or 2) speciation in progress (“parapatric speciation”) 5

Example of Hybrid Zone between western and eastern “subspecies” of the Northern Flicker Futuyma, 1998, p. 258 6

Example of Hybrid Zone (newer generic name is Aspidoscelis) Cnemidophorus tigris The genus Cnemidophorus includes several species, some of which have several subspecies. 7

Example of Hybrid Zone Stebbins, R. C. 1985. A field guide to western reptiles and amphibians. 2 nd ed. Boston, Houghton Mifflin. Range map for six named subspecies of Cnemidophorus tigris. Two exhibit a narrow hybrid zone near AZ-NM border. 8

Example of Hybrid Zone Sampling across the hybrid zone reveals a steep transition in allele frequencies at loci that code for allozymes. Also termed “stepped clines. ” Morphological traits show a similar pattern. Repeated cycles of climatic change seem to have caused cycles of contact vs. separation by unsuitable habitat. Forms on either side may be “subspecies, ” “semispecies” or true species. 9

Example of a Hybrid Between two Species Dark-eyed Junco White-throated Sparrow Hybrid 10

Example of a hybrid between two species 11

Junco Sparrow Hybrid Song of hybrid is intermediate. Would it be attractive to neither or both “parental” species? This will have a huge effect on the potential for gene flow back into the parental species (introgression). 12

Character Displacement Originally, a pattern, in a narrow contact zone between two closely related species – the species are more different in sympatry (where they occur together) than in allopatry 13

Character Displacement in Galapagos Finches The best known case of character displacement occurs between the finches Geospiza fuliginosa and G. fortis. When they occur together, G. fuliginosa has a much narrower beak that G. fortis, and the former eats smaller seeds: the resource is partitioned. When found on separate islands, both species have beaks of intermediate size, and exploit a wider variety of seeds. These inter-population differences might have evolved in response to interspecific competition. 14

Character Displacement in Galapagos Finches When a third species occurs with them, it has a much deeper beak 15

Character Displacement in Stag Beetles Kawano, K. 2003. Character displacement in stag beetles (Coleoptera: Lucanidae). Annals of the Entomological Society of America 96: 503 -511. Abstract. I quantitatively analyzed male morphology of two closely related stag beetles species (Odontolabis mouhoti Hope and O. cuvera Parry) in 11 allopatric and two sympatric locations in the Asian tropics and subtropics. Across allopatric locations, body size and genitalia size nearly completely overlapped between O. mouhoti and O. cuvera, and body color was more similar between the two species in allopatric locations. In sympatric locations the differences between the two species in these characters were highly noticeable, genitalia size being most significant. The body color difference between the two species was most striking in sympatric locations. It is probable that the interaction between the two species induced character displacement in sympatry. Character displacement may enable species to maintain themselves as integrated units by minimizing interspecific competition and enhancing reproductive isolation. 16

Character Displacement in Stag Beetles Body length Fig. 3. Top: Body length of O. mouhoti and O. cuvera at allopatric and sympatric sites. (The 5% reliable range of mean of each population is shown by a rectangular box. ) Bottom: Genitalia length of O. mouhoti and O. cuvera at allopatric and sympatric sites. (The 5% reliable range of the mean of each population is shown by a rectangular box. ) Genitalia length Kawano 2003 17

Character Displacement in Stag Beetles Allopatric Sympatric Fig. 1. Geographic distribution of allopatric and sympatric sites for O. mouhoti and O. cuvera, where sampling for this study was successful. Kawano 2003 Fig. 2. Top: Relationship between body length and genitalia length of O. mouhoti in eastern Thailand O. cuvera in Assam where each is allopatric from the other. (Note that the dimensions of the two species overlap with each other. ) Bottom: Relationship between body length and genitalia length of O. mouhoti and O. cuvera at a sympatric location (northern Thailand-I). (Note that the dimensions of the two species are far apart, without any overlap. ) 18

Character Displacement in Stag Beetles Fig. 4. Top: Male O. cuvera (above) and O. mouhoti (below) at allopatric sites (O. cuvera from Assam and O. mouhoti from eastern Thailand). Bottom: The same species at a sympatric location (northern Thailand-I). Shown are three males on the right and a female on the left, at each locality for each species. Genitalia of males are shown immediately below the body. There is a great difference between the two species in body size, genitalia length, and elytral color pattern at the sympatric site. 19

Ring Species “a chain of interbreeding populations, the ends of which overlap but do not interbreed” 20

Ring species: Ensatina in California See Bergstrom & Dugatkin, 2012, pages 467 -469 21

Ensatina spread from north to south, around the valley See Bergstrom & Dugatkin, 2012, pages 467 -469 22

Neighboring forms can interbreed See Bergstrom & Dugatkin, 2012, pages 467 -469 23

… but the forms at the south end are so different that they cannot! 24

Wake, D. B. 1997. Incipient species formation in salamanders of the Ensatina complex. Proceedings of the National Academy of Sciences USA 94: 7761 -7767. 25

Geographic Variation 1. = within-species variation in the phenotype or genotype that shows geographic pattern 2. virtually all characters show geographic variation 3. useful for testing various evolutionary hypotheses 4. important for understanding adaptation and speciation 26

Geographic Variation “. . . the foundation of most evolutionary theory rests upon inferences drawn from geographic variation or upon the verification of predictions made about it. ” Gould, S. J. , and R. F. Johnston. 1972. Geographic variation. Annual Review of Ecology and Systematics 3: 457 -498. 27

Subspecies Geographic Races can be called Subspecies Elaphe obsoleta Elaphe o. bairdi Elaphe o. quadrivittata Elaphe o. lindheimeri Elaphe o. rossalleni Elaphe o. spiloides 28

Subspecies Some Subspecies of the Black Rat Snake Elaphe o. bairdi Elaphe obsoleta Elaphe o. quadrivittata Elaphe o. lindheimeri Elaphe o. rossalleni 29

Subspecies (or species) may be named after people, e. g. , E. Ross Allen, a herpetologist in Florida (1908 -1981) Elaphe o. rossalleni 30

Subspecies However, Subspecies that have been recognized based on color patterns, scale counts, etc. , do not necessarily correspond to patterns of genetic variation (e. g. , allozymes, microsatellite loci, mitochondrial DNA). Example: Burbrink, F. T. , R. Lawson, and J. B. Slowinski. 2000. Mitochondrial DNA phylogeography of the polytypic North American rat snake (Elaphe obsoleta): a critique of the subspecies concept. Evolution 54: 2107 -2118. 31

Subspecies They sampled from throughout the geographic range. 32

Subspecies Abstract. … Mitochondrial DNA analysis of the polytypic snake, Elaphe obsoleta, yields well-supported clades that do not conform to any of the currently accepted subspecies. … Thus, the subspecies of E. obsoleta do not represent distinct genetic lineages. 33

Burbrink et al. , 2000 The Subspecies do not seem to represent separate evolutionary lineages. Elaphe obsoleta We have had convergent evolution of the black coloration in three different lineages. 34

Subspecies Abstract. … Instead, the evidence points to three wellsupported mitochondrial DNA clades confined to particular geographic areas in the eastern United States. This research underscores the potential problems of recognizing subspecies based on one or a few characters. 35

Burbrink et al. 2000, Fig. 5 Evolutionary lineages (clades) seem to have dispersed from southern “Pleistocene refugia” following glacial retreat. 36

Subspecies: an extreme example Distribution of Southern Pocket Gopher (Thomomys umbrinus). These fossorial rodents create extensive burrows, from which they rarely emerge. 215 subspecies are recognized in the southwestern U. S. and northern Mexico. They vary widely in pelage color, often matching the local soil type. Only certain soils are suitable for burrows, so the ranges are highly disjunct. www. mun. ca/biology/scarr/ 37

Clines Cline = gradual change of characters(s) along environmental gradient, i. e. , in some sort of ordered fashion, rather than just a patchwork like the snakes 38

Examples of Clines Bergmann's (1847) Rule: – Within a genus of endothermic vertebrates, the larger species are found in cooler environments. – Mayr (1956, 1963) restricted Bergmann’s rule to variation within species. – Often examined by relating body size to latitude because as you move away from the equator temperature is generally lower. 39

Examples of Clines Bergmann's (1847) Rule in the shor t-tailed weasel (Mustela erminea): skull length is significantly positive correlated with latitude and negatively correlated with temperature 40

Examples of Clines Bergmann's (1847) Rule among species of penguins: Stansfield, 1977 41

Examples of Clines Recent paper: Ashton, K. G. , M. C. Tracy, and A. de Queiroz. 2000. Is Bergmann's rule valid for mammals? American Naturalist 156: 390 -415. 42

Examples of Clines Ashton et al. (2000) examined the relationship between size and latitude as well as between size and temperature within species of mammals. – 78 of 110 species reported a positive correlation between body size and latitude (G = 18. 96, df = 1, P << 0. 001). • Of species that showed a significant relationship between size and latitude, 43 of 57 reported a positive association (P << 0. 001). – 48 of 64 species showed a negative correlation between size & environmental temperature (P << 0. 001). • Of species that showed a significant correlation between size and temperature, 31 of 38 showed a negative correlation (P << 0. 001). 43

Examples of Clines Allen's Rule: extremities shorter where colder Stansfield, 1977 44

Examples of Clines Allen's Rule: extremities shorter where colder Strickberger, 2000 45

Examples of Clines These sorts of patterns are thought to indicate the past action of natural selection and hence adaptation to environmental factors. However, direct environmental effects can mimic these! Example: Weaver, M. E. , and D. L. Ingram. 1969. Morphological changes in swine associated with environmental temperature. Ecology 50: 710 -713. 46

Direct Environmental Ef fects Can mimic some classic clines! Weaver, M. E. , and D. L. Ingram. 1969. Morphological changes in swine associated with environmental temperature. Ecology 50: 710 -713. 47

Direct Environmental Ef fects Weaver, M. E. , and D. L. Ingram. 1969. Morphological changes in swine associated with environmental temperature. Ecology 50: 710 -713. 48

Direct Environmental Ef fects Weaver, M. E. , and D. L. Ingram. 1969. Morphological changes in swine associated with environmental temperature. Ecology 50: 710 -713. Take-home message: Be cautious about any data on clines or on other forms of geographic variation that do not pertain to organisms reared under common conditions -- the variation may not reflect genetic differences! And, as we discussed previously, you also need to be somewhat cautious about differences among species that were not raised under common-garden conditions. 49

Examples of Clines Gloger's Rule: birds and mammals are darker in more humid environments (Hengeveld 1990) – Sometimes stated as: darker in color towards warmer climates at lower altitudes or lower latitudes, and lighter in color towards colder climates at higher altitudes or higher latitudes. 50

Examples of Clines Gloger's Rule: 51

Examples of Clines Gloger's Rule in human skin color: Strickberger, 2000 Is this strong evidence for genetically based climatic adaptation? 52

Examples of Clines Gloger's Rule in human skin color: Variation is presumably adaptive as protection against ultraviolet rays and melanoma and/or prevention of excess production of vitamin D, which stimulates uptake of calcium in the small intestine. – rickets is caused by too little vitamin D – African American children in U. S. used to have more rickets than did Caucasians – after synthetic vitamin D was invented at the University of Wisconsin in the 1930 s, its routine addition to milk eliminated the problem The ability to tan is a physiological (non-inherited) adaptation (example of phenotypic plasticity) that is also an evolutionary (inherited) adaptation. 53

The Classic Common Garden Experiment The yarrow plant (Achillea) in California, part of the daisy family (Asteracea) Clausen, J. , D. D. Keck, and W. M. Hiesey. 1940. Experimental studies on the nature of species. I. The effect of varied environments on western American plants. Carnegie Inst. Washington Publ. 520. Clausen, J. , D. D. Keck, and W. M. Hiesey. 1948. Experimental studies on the nature of species III: environmental responses of climatic races of Achillea. Carnegie Institute of Washington Publication 581: 1 -129. 54

The Classic Common Garden Experiment The yarrow plant (Achillea) in California Strickberger 2000 55

The yarrow plant (Achillea) in California 10, 000 feet Plants grown at or near their native altitude tend to do the best there = evidence of local adaptation 4, 600 feet Sea Level Strickberger 2000 56

The Classic Common Garden Experiment The yarrow plant (Achillea) in California Take-home message: Populations of this species do show clear evidence of genetic (evolutionary) adaptation to local conditions. Each population does best when grown where it came from. 57

A Recently-evolved Cline in Drosophila Ray Huey Pages 308 -309 58

A Recently-evolved Cline in Drosophila subobscura was accidentally introduced to the New World two decades ago. Once here, it rapidly spread. 59

A Recently-evolved Cline in Drosophila In the Old World, it shows a latitudinal cline in wing size: the further north, the larger the wings. Ten years postintroduction, no such pattern was apparent in North America. 60

A Recently-evolved Cline in Drosophila Females Males A common-garden experiment revealed that by 2000, North American populations showed the same latitudinal gradient as Old World ones: the further north, the larger the wings. 61

A Recently-evolved Cline in Drosophila But the causes are different on each continent. The same pattern has evolved from different “building blocks” = “multiple solutions. ” 62

Extra Slides Follow 63

GOOD SPECIES DESPITE MASSIVE HYBRIDIZATION: GENETIC RESEARCH ON THE CONTACT ZONE BETWEEN THE WATER SNAKES NERODIA SIPEDON AND N. FASCIATA IN THE CAROLINAS, USA 2008. Molecular Ecology 17: 1918 -1929 Konrad Mebert Abstract: Genomic markers generated with the amplified fragment length polymorphism method revealed extensive, panmictic-like hybridization along the narrow contact zone between the Water Snakes Nerodia sipedon and Nerodia fasciata in the Carolinas, USA. However, asymmetric distributions of diagnostic markers between both species and low frequencies of backcrossed hybrids with a high value of interspecific mixture infer selection against certain genotypes. This is consistent with a pronounced genetic and morphological preponderance of N. fasciata characters in the hybrid zone. Despite massive hybridization within the contact zone, the existence of nearly fixed genetic markers and the potential inferiority of certain hybrid genotypes support the species status of the two taxa and corroborate known, but nondiagnostic differences in morphology and ecology. This study stretches the applicability of species concepts to cases where the genetic compatibility between two closely related species is very high, yet, they still evolve and persist as independent entities. ***** A gratis PDF of this article is available from the CNAH PDF Library at http: //www. cnah. org/cnah_pdf. asp 64

Another ring species example: This example was deleted for Fall 2012 because I was running over from the previous CM lecture … 65

Several forms ring the Tibetan Plateau 66

The bird is not found in the center, a high, hostile mountain area Tibetan Plateau 67

Spread has been from the south Tibetan Plateau 68

The gap results from recent human activities. Birds on both sides are similar. 69

Each form has a different song 70

The only neighboring forms that cannot interbreed live where the circle meets 71

Summary 72